A directional control valve such as a control valve or a check valve is used for making air flow in an air pressure pipe, stopping its flow, and changing directions of its flow. Of the directional control valves, the valve which opens/closes the flow path by controlling the current carried to the solenoid is called a solenoid valve.
The solenoid comprises a coil, a column, and a plunger, wherein when the current is carried to the coil, the plunger is attracted by the magnetized column and, in cooperation with such attraction, a main valve thereof can be shifted. A type of main valve includes a poppet type in which a valve body moves a vertical direction of its valve seat so as to open/close the flow path, a spool type in which the valve body inscribed on a cylinder moves axially so as to open/close the flow path, and a slide type in which the valve body having the valve seat moves on a sliding surface so as to open/close the flow path.
The poppet type of solenoid valve has a plunger provided with the valve body, and a spring member by which a spring force in a direction of closing the valve seat is applied to the valve body, so that when the current is carried to the coil, the valve body attracted by the column causes the valve seat to open against the spring force and when no current is carried, the valve body causes the valve seat to close by the spring force. When the valve body of poppet type is formed of an elastic body such as synthetic rubber, if biased to the valve seat, the valve body is elastically deformed, so that a hermetically-closed property of the valve seat can be enhanced.
In previous plungers, there is a plunger in which a concave portion is processed in one end portion of the plunger opposite to the valve seat and an inner circumferential surface of the concave portion is coated with an adhesive agent and an elastic body such synthetic rubber is baked as a valve body to the concave portion (see Patent Document 1). Further, in the previous plungers, there is a plunger in which an accommodating chamber is processed in a tip portion of the plunger and the valve body and a spring member for applying a pressing force to the valve body are incorporated in this accommodating chamber (see Patent Document 2).
Patent Document 1: Japanese Patent Laid-Open Publication No. 2001-280519
Patent Document 2: Japanese Patent Laid-Open Publication No. 11-125357